JP2010027506A - Fuel cell electrode catalyst and its manufacturing method, and solid polymer fuel cell using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell electrode catalyst having higher initial power generating performance (higher activity) than a conventional platinum alloy catalyst while satisfactorily suppressing (enduring) performance degradation after long-time power generating operation, and to provide its manufacturing method and a solid polymer fuel cell using the same. <P>SOLUTION: The fuel cell electrode catalyst is formed of a nonnoble metal alloy which can be complexed with noble metal-carbon supported on a conductive carbon carrier. Herein, the conductive carbon carrier is complexed with a nonnoble metal component and the complexed nonnoble metal component is alloyed with a noble metal component. The fuel cell electrode catalyst is manufactured in a method which includes a first step of complexing the conductive carbon carrier with the nonnoble metal component which can be complexed with carbon fired, a second step of cleaning the complexed material obtained in the first step, and a third step of alloying the complexed nonnoble metal component with the noble metal component. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electrode catalyst for a fuel cell that improves the power generation performance of a conventional platinum alloy catalyst, a method for producing the same, and a polymer electrolyte fuel cell using the same.

  As a cathode and an anode catalyst of an electrode catalyst of a polymer electrolyte fuel cell, a catalyst in which a noble metal such as platinum or a platinum alloy is supported on carbon black has been used. An electrode of a polymer electrolyte fuel cell is prepared by dispersing platinum-supported carbon black in a polymer electrolyte solution, preparing an ink, applying the ink to a gas diffusion substrate such as carbon paper, and drying. . An electrolyte membrane-electrode assembly (MEA) is assembled by sandwiching a polymer electrolyte membrane between these two electrodes and performing hot pressing.

  Platinum is an expensive noble metal and it is desired to exhibit sufficient performance with a small amount of support. Therefore, studies have been made to increase the catalytic activity with a smaller amount. For example, Patent Document 1 listed below has excellent cathode polarization characteristics, and platinum and platinum are used in the cathode catalyst layer for the purpose of obtaining high battery output. In addition to the metal catalyst selected from the group consisting of platinum alloys, the polarization characteristics at the cathode are improved by containing a metal complex having a predetermined amount of iron or chromium. Specifically, a solid polymer fuel cell comprising an anode, a cathode, and a polymer electrolyte membrane disposed between the anode and the cathode, the cathode comprising a gas diffusion layer and the gas diffusion layer A catalyst layer disposed between the layer and the polymer electrolyte membrane, wherein the catalyst layer contains a noble metal catalyst selected from the group consisting of platinum and a platinum alloy, and a metal complex containing iron or chromium. In addition, the metal complex is contained in an amount of 1 to 40 mol% of the total amount of the metal complex and the noble metal catalyst.

  In addition, in Patent Document 2 below, for the purpose of preventing the oxidation of the surface of carbon as a catalyst carrier and improving the durability performance of the electrode catalyst for fuel cells, (1) a raw material compound of metal M and carbon particles And a method for producing an electrode catalyst for a fuel cell comprising a first step of obtaining composite particles containing metal M and carbon, and a second step of supporting a catalyst on the composite particles, (2) A first step of obtaining a composite particle A containing metal M and carbon by mixing a raw material compound of metal M and carbon particles, and a composite containing metal oxide and carbon by oxidizing the composite particle A A method for producing a fuel cell electrode catalyst comprising a second step of obtaining particles B and a third step of supporting the catalyst on the composite particles B is disclosed.

  The catalysts described in Patent Documents 1 and 2 have insufficient hydrogen reduction performance and durability, and it has been desired to develop a catalyst having higher performance and superior durability.

JP 2002-15744 A JP 2007-117862 A

  A large amount of noble metal (platinum) is used for the electrode catalyst of the polymer electrolyte fuel cell. For that purpose, it is an important subject to suppress the performance degradation after long-term power generation operation. The cause of the decrease in performance is mainly a decrease in active sites due to elution of precious metals (mainly platinum) from the catalyst. In order to suppress the performance degradation, it is necessary to suppress the elution of the noble metal and suppress the decrease of the active sites.

  Therefore, the present invention provides an electrode catalyst for a fuel cell that overcomes the deterioration in performance after long-term power generation operation (durability) as well as improved initial power generation performance (high activity) than conventional platinum alloy catalysts, and a method for producing the same. An object of the present invention is to provide a solid polymer fuel cell used.

  In order to increase the activity and durability of an electrode catalyst for a polymer electrolyte fuel cell, a noble metal has been conventionally alloyed. In general, by alloying, an improvement in activity is expected due to the effect of the alloy type of the electrode catalyst. Furthermore, the increase in particle size due to alloying is expected to increase the stability of the catalyst particles and improve the durability.

  The present inventors suppress the elution of the noble metal in which the interaction of carbon + non-noble metal + noble metal is one of the deterioration of the catalyst by alloying the noble metal component with the non-noble metal component compounded on the conductive carbon support. As a result, the present invention has been found.

  That is, first, the present invention is an invention of a fuel cell electrode catalyst comprising a non-noble metal alloy that can be combined with a noble metal-carbon supported on a conductive carbon support, wherein the conductive carbon support and the non-noble metal component And the composite non-noble metal component and noble metal component are alloyed.

  The noble metal component used in the fuel cell electrode catalyst of the present invention is selected from platinum group metals such as platinum, ruthenium and iridium. The non-noble metal used in the present invention is selected from a transition metal or a rare earth metal having a non-noble metal and a stable carbon structure based on the phase diagram of the non-noble metal and carbon. Specifically, manganese (Mn), chromium (Cr), cerium (Ce), molybdenum (Mo), iron (Fe), niobium (Nb), silicon (Si), titanium as non-noble metals that can be combined with carbon One or more types selected from (Ti) and tantalum (Ta) are preferably exemplified.

  Second, the present invention is an invention of a method for producing a fuel cell electrode catalyst comprising a non-noble metal alloy capable of being combined with a noble metal-carbon supported on a conductive carbon support, wherein the conductive carbon support and carbon A first step of firing and compositing a non-noble metal component that can be combined, a second step of cleaning the composite obtained in the first step, and a third step of alloying the combined non-noble metal component and the noble metal component Process.

  In the method for producing a fuel cell electrode catalyst of the present invention, it is preferable to perform hydrogen bubbling and nitrogen bubbling in the third step.

  Examples of the noble metal and non-noble metal that can be combined with carbon used in the production of the fuel cell electrode catalyst of the present invention are as described above.

  Thirdly, the present invention is a polymer electrolyte fuel cell comprising the above fuel cell electrode catalyst as an anode catalyst and / or a cathode catalyst.

  By baking and compounding a conductive carbon support and a non-noble metal (metal particles) that can be combined with carbon under certain conditions, the metal particles have a structure that does not easily dissolve from the conductive carbon support. Next, since metal particles that have not been combined are removed by washing, the metal particles in the composite are only those that do not easily fall off. Since the noble metal, which is the catalyst metal component, is more easily supported on the metal particles than the catalyst carrier, the catalyst metal component is selectively supported on the metal particles in the composite. Furthermore, the alloying enables the metal particles in the composite and the catalyst metal to be integrated.

  As a result, the fuel cell electrode catalyst of the present invention is highly active and superior in durability as compared with conventional noble metal alloy catalysts such as platinum alloys for fuel cells.

  Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples.

[Example: Preparation of Pt-Mn / C catalyst]
A catalyst in which a platinum manganese alloy was supported on carbon (Pt—Mn / C catalyst) was prepared by the following procedure.
Example 1
4.5 g of a commercial product KetjenEC (trade name, manufactured by Ketjen Black International) and Mn nitrate were mixed so that the amount of Mn was 1 g, and stirred for 2 hours. The solution was neutralized and supported with 0.1N ammonia to support Mn on carbon black. This was heat-treated at 1000 ° C. for 5 hours to obtain a Mn / C support.

  Mn / C after firing was washed with 1.0N nitric acid, filtered and dried. In a state where Mn is supported on carbon, it is removed from the carbon by washing with nitric acid. Mn / C of the obtained dry powder was 5.0 g, and it was confirmed that 0.2 g of Mn was combined with C. The presence of Mn was also confirmed by fluorescent X-ray analysis (XRF).

  5.0 g of this powder was added to 1.8 L of pure water, and after hydrogen bubbling, nitrogen bubbling was performed and dispersed.

  To this dispersion, a hexahydroxo platinum nitric acid solution containing 5.0 g of platinum was dropped and sufficiently stirred with carbon. To this, about 100 mL of 0.1N ammonia was added to adjust the pH to about 10 to form hydroxides, which were deposited on carbon, and further reduced at 90 ° C. using ethanol. This dispersion was filtered and dried, and the resulting powder was reduced in hydrogen gas at 400 ° C. for 2 hours, and then alloyed by holding in nitrogen gas at 1000 ° C. for 10 hours to obtain a catalyst powder.

  The platinum loading density of the obtained catalyst powder was confirmed that Pt was not detected from the waste liquid analysis, and that all the Pt was loaded. Pt: 50 wt%, Mn: 2.0 wt%, C: 48 wt%. It was. Furthermore, the particle size of the catalyst was calculated from the peak position of the XRD Pt (111) plane (Scherrer formula), which was 5.2 nm, and the peak of the Pt (111) plane near 39 ° was shifted to the wide angle side. The solid solution (alloying) of the additive element was confirmed.

(Example 2)
The catalyst obtained in Example 1 was stirred with 1.0 N nitric acid. Stirring was performed at room temperature for 2 hours. The stirred solution was filtered, and it was Pt: 50 wt%, Mn: 1.9 wt%, and C: 48.1 wt% from waste liquid analysis (quantification of Mn) of the filtrate.

(Comparative Example 1)
A hexahydroxo platinum nitric acid solution containing 4.2 g of KetjenEC (trade name, manufactured by Ketjen Black International) and 5.0 g of platinum and Mn nitrate were adjusted to 0.8 g of Mn and dispersed in 0.5 L of pure water. About 100 mL of 0.1N ammonia was added thereto to adjust the pH to about 10, and hydroxides were formed and precipitated on carbon. The dispersion was filtered, and the obtained powder was vacuum-dried at 100 ° C. for 10 hours. Next, reduction treatment was carried out by holding at 400 ° C. for 2 hours in hydrogen gas, and then alloying was carried out by holding at 1000 ° C. for 10 hours in nitrogen gas to obtain a catalyst powder.

  The platinum loading density of the obtained catalyst powder was not detected from the waste liquid analysis, and it was confirmed that all the Pt was loaded. Pt: 50 wt%, Mn: 8.0 wt%, C: 42 wt% It was. Furthermore, the particle size of the catalyst was calculated from the peak position of the XRD Pt (111) plane (Scherrer formula), which was 4.9 nm, and the peak of the Pt (11) plane near 39 ° was shifted to the wide angle side. The solid solution of the added element was confirmed.

(Comparative Example 2)
The catalyst obtained in Comparative Example 1 was stirred with 1.0 N nitric acid. Stirring was performed at room temperature for 2 hours. The stirred solution was filtered, and it was Pt: 50 wt%, Mn: 1.8 wt%, and C: 48.2 wt% from waste liquid analysis (Mn determination) of the filtrate.

(Comparative Example 3)
4.8 g of a commercial product KetjenEC (trade name, manufactured by Ketjen Black International) and Mn nitrate were mixed so that the amount of Mn was 0.2 g, and stirred for 2 hours. The solution was neutralized and supported with 0.1N ammonia to support Mn on carbon black. This was heat-treated at 100 ° C. for 5 hours to obtain a Mn / C support. A PtMn / C catalyst was obtained in the same manner as in Example 1 without performing this acid treatment of Mn / C. The physical properties of the obtained catalyst were Pt: 50 wt%, Mn: 2.0 wt%, and C: 48 wt%.

[Performance evaluation]
(Initial performance measurement)
In order to compare the catalyst performance in the initial stage, the initial voltage measurement was performed as follows. The cell temperature of the single cell is set to 80 ° C., the humidified air that has passed the heating bubbler to the cathode side electrode is RH100, the stoichiometric ratio is 7.5, and the humidified hydrogen that has been passed through the heating bubbler to the anode side electrode is RH100 was supplied at a stoichiometric ratio of 7.5, and current-voltage characteristics were measured using an electronic load. The Pt amount of each electrode was 0.3 mg / cm ² .

(Durability test method)
After the initial voltage measurement, an endurance test (carbon accelerated deterioration test) was performed under the following conditions. The cell temperature of the single cell is set to 80 ° C., the humidified air that has passed the heating bubbler to the cathode side electrode is RH100, the stoichiometric ratio is 7.5, and the humidified hydrogen that has passed the heating bubbler to the anode side electrode is RH100 was supplied at a stoichiometric ratio of 7.5. Current value is varied every 5 seconds OCV and 0.1 A / cm ² and the voltage characteristics at 0.1 A / cm ² after 2000hr was performance after endurance.

  Table 1 summarizes the results. FIG. 1 shows the relationship between endurance time and battery voltage in Examples and Comparative Examples.

  The catalysts of Examples 1 and 2 of the present invention are excellent in initial power generation performance and performance deterioration suppression (durability) after long-term power generation operation, whereas the catalysts of Comparative Examples 1 to 3 are particularly inferior in durability. ing.

  The catalyst of the present invention is characterized in that Pt is alloyed with Mn / C, and is shown in an image diagram of a difference from conventional PtMn / C. FIG. 2 is an image diagram of the catalysts of Examples 1 and 2. FIG. 3 is an image diagram of the catalysts of Comparative Examples 1 and 2. FIG. 4 is an image diagram of the catalyst of Comparative Example 3.

  In the PtMn / C of the present invention, since Pt is alloyed in a state where carbon and Mn are composited, the PtMn is firmly fixed on the carbon by the anchor effect. As a result, as shown in FIG. 1, no performance degradation after the durability test was confirmed. That is, Mn and carbon are combined by firing, and Pt is supported thereon. Further, Pt is selectively supported on the activated Mn by performing hydrogen bubbling and nitrogen bubbling. Therefore, it is considered that Mn is difficult to dissolve.

  On the other hand, in conventional PtMn / C, PtMn is supported on carbon. Therefore, compared with Example 1 and Example 2, it is a structure which is easy to melt | dissolve, Therefore It is thought that the performance fall by the reduction | decrease of the active point by alloy collapse has occurred. Further, it is considered that PtMn tends to cause sintering by moving laterally on the carbon.

  In the catalyst of Comparative Example 3, in which Mn and carbon were calcined and then Pt was supported and alloyed without acid treatment, Mn / C after calcining was not acid-treated. Since Mn / C which is not converted is mixed, it is considered that the performance deterioration as shown in FIG. 1 has occurred.

  In Examples 1 and 2, Mn and carbon are combined by firing. It can be seen that Mn supported on carbon is completely dissolved by acid treatment, whereas it is compounded by firing. In addition, there are transition metals such as Ni that do not composite even when fired. FIG. 5 shows the relationship between the cleaning time and the amount of metal when Ni is supported on carbon as compared with Mn. The firing temperature was 1000 ° C., and the acid was 1.0N nitric acid. From the results of FIG. 5, it can be seen that Ni does not form a composite with carbon even when fired.

  The fuel cell electrode catalyst of the present invention has improved initial power generation performance (higher activity) than the conventional platinum alloy catalyst and overcame performance degradation suppression (durability) after long-term power generation operation. This contributes to the spread of fuel cells.

The relationship of the endurance time and battery voltage of an Example and a comparative example is shown. It is an image figure of the catalyst of Example 1 and 2. FIG. It is an image figure of the catalyst of the comparative examples 1 and 2. 4 is an image diagram of a catalyst of Comparative Example 3. FIG. The relationship between the cleaning time and the amount of metal when Ni is supported on carbon as compared with Mn is shown.

Claims (6)

  A non-noble metal electrode catalyst for a fuel cell comprising a noble metal-carbon alloy capable of being combined with a noble metal-carbon supported on a conductive carbon support, wherein the conductive carbon support and a non-noble metal component are combined and combined An electrode catalyst for a fuel cell, wherein a component and a noble metal component are alloyed.   Non-noble metals that can be combined with the carbon are manganese (Mn), chromium (Cr), cerium (Ce), molybdenum (Mo), iron (Fe), niobium (Nb), silicon (Si), titanium (Ti), The electrode catalyst for fuel cells according to claim 1, wherein the electrode catalyst is one or more selected from tantalum (Ta).   A method for producing an electrode catalyst for a fuel cell comprising a noble metal-alloy capable of being combined with a noble metal-carbon supported on a conductive carbon support, wherein the conductive carbon support and a non-noble metal component capable of being composited by firing carbon A fuel cell electrode catalyst, comprising: a first step of compounding the second step; a second step of cleaning the composite obtained in the first step; and a third step of alloying the combined non-noble metal component and noble metal component. Manufacturing method.   The method for producing a fuel cell electrode catalyst according to claim 3, wherein hydrogen bubbling and nitrogen bubbling are performed in the third step.   Non-noble metals that can be combined with the carbon are manganese (Mn), chromium (Cr), cerium (Ce), molybdenum (Mo), iron (Fe), niobium (Nb), silicon (Si), titanium (Ti), The method for producing an electrode catalyst for a fuel cell according to claim 3 or 4, wherein the method is one or more selected from tantalum (Ta).   A polymer electrolyte fuel cell comprising the fuel cell electrode catalyst according to claim 1 or 2 as an anode catalyst and / or a cathode catalyst.

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